This project is concerned with the mechanism of coupling of macromolecule and electrolyte (fluid) secretion in the pancreas and parotid, using the rat as model. Our recent investigations of the electrolyte permeability properties of the membrane of isolated zymogen granules have demonstrated the presence of chloride (anion) transport pathways, which are activated in situ by pretreatment with secretagogues. Since the granule membrane serves as precursor for the luminal plasma membrane, these findings suggest that chloride secretion occurs across the granule membrane after its fusion with the plasma membrane and that the resulting fluid secretion serves to flush out the digestive enzymes from the former intragranular space. This mechanism would automatically couple fluid and macromolecule secretion. This proposal is specifically concerned with quantitative measurements of the chloride permeability of granule membranes, an evaluation of intracellular_signals involved in activation of its chloride permeability, and the biochemical changes in the membrane associated with activation. These goals will be accomplished by measuring the electrical and transport properties of isolated granule membranes, by comparison of the biochemical composition of membranes from isolated resting and secretagogue-activated granules, and by investigations of the activation process in an isolated rat pancreatic acinar preparation. The results should provide answers about contributions of the zymogen granule membrane to electrolyte secretion and about the intracellular signals and enzymes involved in normal activation_of chloride conductance in the luminal plasma membrane. The biochemical studies may also provide molecular information on the chloride transporters involved and the chemistry of their activation. Information of these processes is important for understanding the cell physiology of exocrine secretion and its pathophysiology as expressed, for example, in Cystic Fibrosis (CF) in the form of viscous secretions and ductal blockage of the pancreas.